A die paste has a wide application as an adhesive used in stacking chips or attaching a chip to a support member such as PCB or a lead-frame in a semiconductor device packaging process.
In a certain type semiconductor package, a semiconductor die or chip is mechanically connected to a substrate by an adhesive, and an electrical connection is established between the semiconductor die or chip and the substrate. The substrate is connected to another electrical device or an external power source. The semiconductor package may be manufactured by a series of steps. Alternatively, a semiconductor die or chip is mechanically connected to a substrate by an adhesive, and may be preserved for a predetermined period of time.
In the case that a semiconductor package is manufactured by a series of steps, an adhesive is applied on a substrate, a semiconductor chip is attached to the adhesive and the adhesive is cured by heat or both of heat and pressure. A solvent-free liquid or paste type adhesive or a solid type adhesive may be appropriate. The liquid or paste type adhesive is cured and solidified by heating. Meanwhile, in the case that an adhesive is applied on a substrate, a semiconductor packaging process is stopped and an assembly process is deferred to a later time, the adhesive should be solid for complete preservation. A solid type adhesive is liable to minimum or little bleeding and can accurately control the thickness of a bondline, i.e. an interface between the semiconductor chip and the adhesive, and a die tilt.
In some semiconductor package applications, a paste adhesive is preferable to a film adhesive for a procedural reason. However, the paste adhesive requires bondline and fillet control. In this case, an adhesive known as a B-stageable adhesive may be used. In the case that an adhesive material is solid, the solid is dispersed or dissolved in a solvent to form a paste, and the paste is applied on a substrate. Subsequently, the adhesive is heated to vaporize the solvent, so that a non-cured solid type adhesive leaves on the substrate. In the case that an adhesive material is liquid or paste, the adhesive is applied on a substrate, heated and partially cured into a solid state.
Such a die adhesive is applied on a member with a predetermined pattern through screen printing, passes through B-stage curing process, is left for 1 day or more at normal temperature and passes through a preliminary dry process to remove any remaining moisture before die attaching. The preliminary dry process can prevent a void that may occur to the die adhesive due to the moisture remaining in the die adhesive at a subsequent high temperature process, and thus it is indispensable to a conventional semiconductor packaging method. After a die attaching process is completed, a curing process is performed to improve heat resistance and reliability of the die adhesive. Finally, after a wire-bonding process is completed, an encapsulation process using an epoxy molding compound (EMC) is performed to protect the attached chip, and a thermal hardening indispensably process is performed to improve heat resistance and adhesion of the EMC.
As mentioned above, from application of the die adhesive to encapsulation (protection using an encapsulation material), the conventional semiconductor packaging method needs several heating processes. This goes against process efficiency and is not economical. The related industry has attempted to simplify the process, and the present invention was devised under this technical background.